Dynamic spinal rod assembly and method for dynamic stabilization of the spine

Abstract

A versatile dynamic spinal rod and bone anchor assembly for use in a dynamic stabilization system to support the spine while providing for the preservation of spinal motion. Alternative embodiments can be used for spine fusion. The dynamic bone anchor provides load sharing while preserving range of motion and reducing stress exerted upon the bone anchors and spinal anatomy. The dynamic bone anchor includes a deflectable post connected by a ball-joint to a threaded anchor. The dynamic rod connects different levels of the construct in a multilevel construct. The dynamic rod is connected to the dynamic bone anchor by a joint which permits relative movement of the deflectable post and rod reducing the stress exerted upon the bone anchors and spinal anatomy.

1. A spine stabilization system adapted to stabilize a first bone of a spine relative to a second bone of the spine, wherein the spine stabilization system comprises:
 a bone anchor having a post connected to a threaded shaft adapted to engage the first bone of the spine; 
 an elongated spinal rod having a first end, a second end and a longitudinal rod axis; 
 a housing at the first end of the of the elongated spinal rod; 
 a rod bore passing through the housing perpendicular to the rod axis; 
 a spherical pocket within the bore; 
 a ball-shaped mount trapped within the spherical pocket; 
 a ball bore passing through the ball-shaped mount and which ball bore can receive the post of the bone anchor; and 
 wherein the ball-shaped mount is configured to provide a non-locking ball-joint such that the elongated spinal rod may be secured to the bone anchor substantially perpendicular to the longitudinal rod axis while allowing the elongated spinal rod to pivot through a range of motion relative to the bone anchor after securing the elongated spinal rod to the bone anchor. 
 
     
     
       2. The spine stabilization system of  claim 1 , wherein the bone anchor is configured such that the post can deflect relative to the threaded shaft in response to a load placed on the post by the spinal rod. 
     
     
       3. The spine stabilization system of  claim 1 , wherein the spinal rod can pivot relative to the post to compensate for changes in angle of the post relative to the threaded shaft of the bone anchor when the post deflects relative to the threaded shaft in response to a load placed on the post by the spinal rod. 
     
     
       4. The spine stabilization system of  claim 1 , wherein the post can pivot relative to the longitudinal rod axis without applying a bending moment to the spinal rod. 
     
     
       5. The spine stabilization system of  claim 1 , wherein the bone anchor comprises a compliant member which controls deflection of the post relative to the threaded shaft in response to a load placed on the post by the spinal rod. 
     
     
       6. The spine stabilization system of  claim 5 , in combination with a second bone anchor comprising:
 a head including a receiver connected to a threaded shaft adapted to engage the second bone of the spine; and 
 wherein the receiver is configured to be secured to the second end of the elongated spinal rod. 
 
     
     
       7. The spine stabilization system of  claim 6 , wherein the second bone anchor comprises a polyaxial head. 
     
     
       8. The spine stabilization system of  claim 6 , wherein:
 the bone anchor is secured to the ball-shaped mount; and 
 the second bone anchor is secured to the second end of the elongated rod. 
 
     
     
       9. A spine stabilization system adapted to span a spinal segment between a first bone of a spine and a second bone of the spine, wherein the spinal stabilization system comprises:
 a bone screw having a post connected to a threaded shaft adapted to engage the first bone of the spine; 
 the bone screw including a compliant member which allows a deflection of the post relative to the threaded shaft in response to a load on the post; 
 a spinal rod having a first end, a second end and a longitudinal rod axis; 
 a non-locking ball-joint at the first end of the spinal rod; 
 the ball-joint comprising a bore that can receive the post of the bone screw; and 
 whereby the post of the bone screw may be secured to the spinal rod at an angle substantially perpendicular to the longitudinal rod axis; and 
 such that when the post of the bone screw is secured to the ball-joint, the ball-joint still allows deflection of the post relative to the threaded shaft of the bone screw without applying a bending moment to the spinal rod. 
 
     
     
       10. The spine stabilization system of  claim 9 , wherein:
 the deflection of the post relative to the threaded shaft of the bone screw changes an angle between the post and the threaded shaft of the bone screw; and 
 the ball-joint is configured such that the spinal rod may pivot relative to the post sufficiently to compensate for changes in the angle between the post and the threaded shaft of the bone screw. 
 
     
     
       11. The spine stabilization system of  claim 9 , wherein the ball-joint is adapted to permit the spinal rod to rotate relative to the bone screw. 
     
     
       12. The spine stabilization system of  claim 9 , in combination with a second bone screw comprising:
 a polyaxial head including a receiver connected to a threaded shaft adapted to engage the second bone of the spine; and 
 wherein the receiver is configured to be secured to the second end of the elongated spinal rod. 
 
     
     
       13. The spine stabilization system of  claim 9 , wherein:
 the bone screw is secured to the ball-shaped mount; and 
 the second bone screw is secured to the second end of the spinal rod. 
 
     
     
       14. The spine stabilization system of  claim 9 , in combination with a second bone screw comprising:
 a head including a receiver connected to a threaded shaft adapted to engage the second bone of the spine; and 
 wherein the receiver is configured to be secured to the second end of the spinal rod. 
 
     
     
       15. A method for implanting a spinal stabilization system, adapted to span a spinal segment between a first bone of a spine and a second bone of the spine, wherein the spinal stabilization system comprises:
 a bone screw having a post connected to a threaded shaft adapted to engage the first bone of the spine; 
 the bone screw including a compliant member which allows a deflection of the post relative to the threaded shaft in response to a load on the post; 
 a spinal rod having a first end, a second end and a longitudinal rod axis; 
 a non-locking ball-joint at the first end of the of the spinal rod; 
 the ball-joint comprising a bore that can receive the post of the bone screw; and 
 whereby the post of the bone screw may be secured to the spinal rod at an angle substantially perpendicular to the longitudinal rod axis; and 
 such that when the post of the bone screw is secured to the ball-joint, the ball-joint still allows deflection of the post relative to the threaded shaft of the bone screw without applying a bending moment to the spinal rod; and 
 in combination with a second bone screw comprising: 
 a head including a receiver connected to a threaded shaft adapted to engage the second bone of the spine; and 
 wherein the receiver is configured to be secured to the second end of the spinal rod; and 
 the method comprising the steps of: 
 
       (a) implanting the bone screw in the first bone of the spine; 
       (b) implanting the second bone screw in the second bone of the spine; 
       (c) after performing steps (a) and (b), securing the ball joint to the post of the first bone screw such that after said securing the spinal rod is pivotally connected to the post thereby allowing the deflection of the post relative to the threaded shaft of the bone screw without applying a bending moment to the spinal rod; and 
       (d) after performing step (c), securing the spinal rod to the receiver of the head of the second bone screw. 
     
     
       16. A spinal implant comprising:
 a bone screw having a post connected to a threaded shaft adapted to engage a first bone of the spine; 
 the bone screw including a compliant member which allows a deflection of the post relative to the threaded shaft in response to a load on the post; 
 an elongated rod having a first end, a second end and a longitudinal rod axis; 
 a mount, with a bore to secure the mount to the post of the bone screw such that the post forms an angle with the longitudinal rod axis; and 
 the mount being pivotally connected to the elongated rod such that after securing the mount to the post of the bone screw the angle between the post and the longitudinal rod axis may vary between 85 and 105 degrees. 
 
     
     
       17. The spinal implant of  claim 16 , wherein the angle between the post and the longitudinal rod axis can vary between 85 and 105 degrees without exerting a bending moment on the elongated spinal rod. 
     
     
       18. The spinal implant of  claim 16 , wherein the mount is secured to the post of the bone screw by a fastener. 
     
     
       19. A method for implanting a spinal stabilization system wherein the spinal stabilization system comprises:
 a bone screw having a post connected to a threaded shaft adapted to engage a first bone of the spine; 
 the bone screw including a compliant member which allows a deflection of the post relative to the threaded shaft in response to a load on the post; 
 an elongated rod having a first end, a second end and a longitudinal rod axis; 
 a mount, with a bore to secure the mount to the post of the bone screw such that the post forms an angle with the longitudinal rod axis; and 
 the mount being pivotally connected to the elongated rod such that after securing the mount to the post of the screw, the angle between the post and the longitudinal rod axis may vary between 85 and 105 degrees; and 
 
       the method comprising the steps of: 
       (a) implanting the bone screw in the first bone of the spine; 
       (b) implanting a polyaxial bone screw in the second bone of the spine; 
       (c) after performing step (a), securing the mount to the post of the bone screw such that after said securing the elongated rod is pivotally connected to the post such that the angle between the post and the longitudinal rod axis may still vary between 85 and 105 degrees; and 
       (d) after performing steps (b) and (c), securing the second end of the elongated rod to the polyaxial bone screw.